[llvm] Explain partial byte extraction logic. (PR #92868)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-nvptx

Author: Johannes Reifferscheid (jreiffers)

<details>
<summary>Changes</summary>

This is a follow-up to #<!-- -->92506.

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Full diff: https://github.com/llvm/llvm-project/pull/92868.diff


1 Files Affected:

- (modified) llvm/lib/Target/NVPTX/NVPTXAsmPrinter.cpp (+4) 


``````````diff
diff --git a/llvm/lib/Target/NVPTX/NVPTXAsmPrinter.cpp b/llvm/lib/Target/NVPTX/NVPTXAsmPrinter.cpp
index f63697916d902..c30368a60c126 100644
--- a/llvm/lib/Target/NVPTX/NVPTXAsmPrinter.cpp
+++ b/llvm/lib/Target/NVPTX/NVPTXAsmPrinter.cpp
@@ -1851,6 +1851,10 @@ void NVPTXAsmPrinter::bufferLEByte(const Constant *CPV, int Bytes,
   auto AddIntToBuffer = [AggBuffer, Bytes](const APInt &Val) {
     size_t NumBytes = (Val.getBitWidth() + 7) / 8;
     SmallVector<unsigned char, 16> Buf(NumBytes);
+    // `extractBitsAsZExtValue` does not allow the extraction of bits beyond the
+    // input's bit width, and i1 arrays may not have a length that is a multuple
+    // of 8. We handle the last byte separately, so we never request out of
+    // bounds bits.
     for (unsigned I = 0; I < NumBytes - 1; ++I) {
       Buf[I] = Val.extractBitsAsZExtValue(8, I * 8);
     }

``````````

</details>


https://github.com/llvm/llvm-project/pull/92868